Discharge lamp lighting device, discharge lamp lighting method, and projector device

ABSTRACT

A discharge lamp lighting device includes a resonant circuit section connected to a discharge lamp, a power conversion section adapted to convert direct-current power into alternating-current power, and then supply the discharge lamp with the alternating-current power via the resonant circuit section, and a control section adapted to change a frequency of the alternating-current power in a stepwise manner with a frequency, which is different from a frequency causing a resonance of the resonant circuit section, intervening between frequency values of the frequency changed in a lighting start period until the discharge lamp reaches a stationary lighting state.

BACKGROUND

1. Technical Field

The present invention relates to a discharge lamp lighting device, adischarge lamp lighting method, and a projector device.

2. Related Art

In the past, there has been known a projector device equipped with adischarge lamp such as a high-pressure mercury lamp as a light source,and this type of projector device is provided with a resonant circuitfor obtaining a high voltage for starting discharge of the dischargelamp (see JP-A-2007-27145 (Document 1)). According to this projectordevice, when lighting the discharge lamp, the high voltage is obtainedby matching the frequency of the alternating-current power supplied tothe discharge lamp with the resonant frequency of the resonant circuit.Further, after the discharge lamp starts discharge to light, thefrequency of the alternating-current power supplied to the dischargelamp is lowered to thereby supply the discharge lamp with a voltage forstationary lighting.

Incidentally, individual difference and aging variation exist in theinductance component and the capacitance component of the resonantcircuit. Therefore, if the frequency of the alternating-current power,which is supplied to the resonant circuit when lighting the dischargelamp, is fixed, there can occur the case in which the resonant fails tooccur, and as a result, the discharge lamp fails to light. In order toavoid such a problem, according to the technology disclosed in Document1, the frequency of the alternating-current power supplied to thedischarge lamp is increased monotonically toward the resonant frequencyto thereby find out the actual resonant frequency in every lightingoperation (see description in, e.g., paragraphs 0076, 0081 of Document1).

However, according to the related art described above of monotonicallyvarying the frequency of the alternating-current power supplied to thedischarge lamp, the resonant circuit is left in a quasi-resonant stateuntil the discharge lamp starts lighting. In such a state, the voltageand the current in the resonant circuit increase, and further, theswitching loss in, for example, a bridge circuit for generating thealternating-current power supplied to the resonant circuit alsoincreases. Therefore, according to the related art described above,there arises a problem that the power consumption when lighting thedischarge lamp increases.

SUMMARY

An advantage of some aspects of the invention is to provide a dischargelamp lighting device, a discharge lamp lighting method, and a projectordevice capable of lighting a discharge lamp while reducing the powerconsumption.

An aspect of the invention is directed to a discharge lamp lightingdevice including a resonant circuit section connected to a dischargelamp, a power conversion section adapted to convert direct-current powerinto alternating-current power, and then supply the discharge lamp withthe alternating-current power via the resonant circuit section, and acontrol section adapted to change a frequency of the alternating-currentpower in a stepwise manner with a frequency, which is different from afrequency causing a resonance of the resonant circuit section,intervening between frequency values of the frequency changed in alighting start period until the discharge lamp reaches a stationarylighting state.

According to the configuration described above, in the process ofchanging the frequency of the alternating-current power supplied to theresonant circuit section, the frequency of the alternating-current poweris temporarily set to the frequency different from the frequency causingthe resonance of the resonant circuit section. Thus, the resonantcircuit section temporarily gets out of the resonant state, and it isarranged that the reactance component of the resonant circuit section istemporarily actualized. Therefore, the voltage and the current in theresonant circuit section are suppressed, and thus the power consumptionin the resonant circuit section is suppressed. Therefore, it becomespossible to light the discharge lamp while suppressing the powerconsumption.

In the discharge lamp lighting device described above, for example, thecontrol section may change the frequency of the alternating-currentpower in a stepwise manner in a descending direction toward thefrequency causing the resonance of the resonant circuit section.

According to the configuration described above, since the resonantcircuit section acts in the capacitive region in the process of changingthe frequency of the alternating-current power in a stepwise manner, thecurrent flowing back from the resonant circuit section to the powerconversion section does not occur in the process of the power conversionsection performing the switching operation. Therefore, it becomespossible to prevent the loss due to the reverse current.

In the discharge lamp lighting device described above, for example, thefrequency different from the frequency causing the resonance of theresonant circuit section may be a frequency lower than the frequencycausing the resonance of the resonant circuit section.

According to the configuration described above, since the resonantcircuit section gets out of the resonant state when the frequency of thealternating-current power is set to the frequency lower than thefrequency causing the resonance of the resonant circuit section, thevoltage and the current in the resonant circuit section can be reduced.In addition, since the frequency of the switching operation in the powerconversion section for supplying the alternating-current power isdecreased, the switching loss in the power conversion section can bereduced.

The discharge lamp lighting device described above may further include,for example, a lighting detection section adapted to detect lighting ofthe discharge lamp, and the control section may change the frequency ofthe alternating-current power in a stepwise manner with the frequency,which is different from the frequency causing the resonance of theresonant circuit section, intervening between the frequency values ofthe frequency changed if lighting of the discharge lamp fails to bedetected by the lighting detection section.

According to the configuration described above, it becomes possible tochange the frequency of the alternating-current power in a stepwisemanner until the lighting detection section detects lighting of thedischarge lamp.

In the discharge lamp lighting device described above, for example, thecontrol section may set the frequency of the alternating-current powerto a predetermined frequency in a stationary lighting state if thelighting detection section detects lighting of the discharge lamp.

According to the configuration described above, it becomes possible tomake the discharge lamp transition to the stationary lighting state.

The discharge lamp lighting device described above may further include,for example, a lighting detection section adapted to detect lighting ofthe discharge lamp, the control section may set the frequency of thealternating-current power in a first time period so that the frequencyof the alternating-current power changes in a stepwise manner with thefrequency, which is different from the frequency causing the resonanceof the resonant circuit section, intervening between frequency values ofthe frequency changing, and the lighting detection section may detectlighting of the discharge lamp in a second time period after the firsttime period.

According to the configuration described above, it becomes possible toperform the stable lighting detection of the discharge lamp.

The discharge lamp lighting device described above may further include,for example, a voltage detection section adapted to detect a resonantvoltage of the resonant circuit section, and if a change in the resonantvoltage detected by the voltage detection section is switched fromincrease to decrease in a process of changing the frequency of thealternating-current power in a stepwise manner, the control section mayset the frequency of the alternating-current power to the frequency in aprevious step.

According to the configuration described above, it becomes possible toset the frequency of the alternating-current power to the vicinity ofthe frequency causing the resonance of the resonant circuit section.

The discharge lamp lighting device described above may further include,for example, a current detection section adapted to detect a resonantcurrent of the resonant circuit section, and if a change in the resonantcurrent detected by the current detection section is switched fromincrease to decrease in a process of changing the frequency of thealternating-current power in a stepwise manner, the control section mayset the frequency of the alternating-current power to the frequency in aprevious step.

According to the configuration described above, it becomes possible toset the frequency of the alternating-current power to the vicinity ofthe frequency causing the resonance of the resonant circuit section.

The discharge lamp lighting device described above may further include,for example, a detection section adapted to detect one of a resonantoutput current and a resonant output voltage of the resonant circuitsection, and a lighting detection section adapted to detect lighting ofthe discharge lamp, and if a change in one of the resonant current andthe resonant voltage detected by the detection section is switched fromincrease to decrease in a first time period in a process of changing thefrequency of the alternating-current power in a stepwise manner, thecontrol section may set the frequency of the alternating-current powerto the frequency in a previous step, and the lighting detection sectionmay detect lighting of the discharge lamp in a second time period afterthe first time period.

According to the configuration described above, it becomes possible toapply alternating-current power with a higher voltage to the dischargelamp.

In the discharge lamp lighting device described above, in the first timeperiod, the control section may apply the frequency in the previous stepset as the frequency of the alternating-current power a predeterminednumber of times before the first time period ends.

According to the configuration described above, it becomes possible toapply alternating-current power with a higher voltage to the dischargelamp.

In the discharge lamp lighting device described above, for example,alternating-current power with a frequency 1/N (N denotes an integer) ofthe frequency of the alternating-current power may be applied to theresonant circuit section.

According to the configuration described above, for example, the greaterthe value of N is, the higher the natural resonant frequency of theresonant circuit section becomes. The higher the natural resonantfrequency of the resonant circuit section is, the smaller the values ofthe inductance component and the capacitance component defining theresonant frequency can be set. Therefore, by using thealternating-current power with the 1/N frequency, it becomes possible toconfigure the resonant circuit section having a small size. Further, byusing the alternating-current power with the 1/N frequency, thefrequency of the alternating-current power supplied to the resonantcircuit section can be set lower relatively to the natural resonantfrequency of the resonant circuit section. Therefore, it becomespossible to stabilize the switching operation of the power conversionsection for supplying the alternating-current power described above.

Another aspect of the invention is directed to a discharge lamp lightingdevice adapted to supply a discharge lamp with alternating-current powervia a resonant circuit section to thereby start discharge of thedischarge lamp to light the discharge lamp including a section adaptedto change a frequency of the alternating-current power in a stepwisemanner with a frequency, which is different from a frequency causing aresonance of the resonant circuit section, intervening between frequencyvalues of the frequency changed in a lighting start period until thedischarge lamp reaches a stationary lighting state.

According to the configuration described above, substantially the samefunctions and advantages as in the discharge lamp lighting deviceaccording to the aspect of the invention described above can beobtained.

In the discharge lamp lighting device described above, for example, thefrequency different from the frequency causing a resonance of theresonant circuit section may be lower than the frequency causing theresonance of the resonant circuit section, and higher than a frequencyat which a current supplied from a power conversion section adapted tosupply the alternating-current power is one of equal to and lower than apredetermined value.

According to the configuration described above, it becomes possible tosuppress the power consumption in the resonant circuit section whilesuppressing the rush current supplied to the discharge lamp.

Still another aspect of the invention is directed to a discharge lamplighting method including converting, by a power conversion section,direct-current power into alternating-current power, and then supplyinga discharge lamp with the alternating-current power via a resonantcircuit section, and changing, by a control section, a frequency of thealternating-current power in a stepwise manner with a frequency, whichis different from a frequency causing a resonance of the resonantcircuit section, intervening between frequency values of the frequencychanged in a lighting start period until the discharge lamp reaches astationary lighting state.

According to the configuration described above, substantially the samefunctions and advantages as in the discharge lamp lighting deviceaccording to the aspect of the invention described above can beobtained.

Yet another aspect of the invention is directed to a projector deviceincluding a discharge lamp as a light source, and any one of thedischarge lamp lighting devices described above as a device adapted tolight the discharge lamp.

According to the configuration described above, substantially the samefunctions and advantages as in the discharge lamp lighting deviceaccording to the aspect of the invention described above can beobtained.

According to the aspects of the invention, it is possible to light thedischarge lamp while suppressing the power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a block diagram showing an example of a functionalconfiguration of a projector device according to a first embodiment ofthe invention.

FIG. 2 is a block diagram showing an example of a functionalconfiguration of a discharge lamp lighting device provided to theprojector device according to the embodiment.

FIG. 3 is an explanatory diagram for explaining an overall operation ofthe discharge lamp lighting device provided to the projector deviceaccording to the embodiment.

FIG. 4 is a waveform chart for supplementarily explaining an overalloperation of the discharge lamp lighting device provided to theprojector device according to the embodiment.

FIG. 5 is a flowchart showing an example of a flow of the operation ofthe projector device according to the embodiment.

FIG. 6 is a block diagram showing an example of a functionalconfiguration of a discharge lamp lighting device provided to aprojector device according to a second embodiment of the invention.

FIG. 7 is an explanatory diagram for explaining an overall operation ofthe discharge lamp lighting device provided to the projector deviceaccording to the embodiment.

FIG. 8 is a waveform chart for supplementarily explaining an overalloperation of the discharge lamp lighting device provided to theprojector device according to the embodiment.

FIG. 9 is a flowchart showing an example of a flow of the operation ofthe projector device according to the embodiment.

FIG. 10 is a table showing an example of a relationship between acurrent value and a skip count according to the embodiment.

FIG. 11 is a diagram showing an example of transition of drive frequencysetting time periods and lighting detection time periods according to athird embodiment of the invention.

FIG. 12 is a diagram showing an example of transition of the drivefrequency in the drive frequency setting time period according to theembodiment.

FIG. 13 is a flowchart showing an example of a flow of the operation ofthe projector device according to the embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

Hereinafter, a first embodiment out of some aspects of embodying theinvention will be explained in detail with reference to the accompanyingdrawings.

It should be noted that the same reference symbols will denote the sameelements throughout all of the embodiment and all of the drawings in thepresent specification.

FIG. 1 is a block diagram showing an example of a functionalconfiguration of a projector device 1 according to the presentembodiment. The projector device 1 according to the present embodimentis provided with a discharge lamp 10 as a light source, liquid crystalpanels 20 for modulating and then transmitting illumination light fromthe discharge lamp 10 in accordance with an image to be projected, and aprojection optical system 30 for projecting the transmitted light, whichis transmitted through the liquid crystal panels 20, on a screen (notshown). Although in the present embodiment, it is assumed that thehigh-pressure mercury lamp using the arc discharge is used as thedischarge lamp 10, the invention is not limited to this example, but anarbitrary discharge lamp such as a metal halide lamp or a xenon lamp canbe used.

Further, the projector device 1 is provided with an interface (I/F)section 40, an image processing section 50, a liquid crystal drivesection 60, a discharge lamp lighting device 70, and a centralprocessing unit (CPU) 80. Among these constituents, the interfacesection 40 is for converting an image signal SP input from a personalcomputer or the like not shown into image data having a format, whichcan be processed by the image processing section 50. The imageprocessing section 50 is for performing a variety of image processingsuch as a luminance adjustment or a balance adjustment on the image datasupplied from the interface section 40. The liquid crystal panel drivesection 60 is for driving the liquid crystal panels 20 based on theimage data on which the image processing is performed by the imageprocessing section 50.

The discharge lamp lighting device 70 is provided with a resonantcircuit section 73 described later functioning as an igniter, andsupplies the discharge lamp 10 with the high-frequencyalternating-current power via the resonant circuit section 73 to therebystart discharge of the discharge lamp to light the discharge lamp 10.The discharge lamp lighting device 70 is configured so as to change thefrequency fs of the alternating-current power supplied from a powerconversion section 72 in a stepwise manner with a predetermined basicfrequency fo, which is different from the frequency causing theresonance of the resonant circuit section 73, intervening therebetweenin the lighting start period until the discharge lamp 10 reaches thestationary lighting state. The details will be described later.

The CPU 80 is for controlling the image processing section 50 and theprojection optical system 30 in accordance with the operation of theoperation button (not shown) provided to the remote controller not shownand the main body of the projector device 1. In the present embodiment,the CPU 80 has a function of instructing the discharge lamp lightingdevice 70 to light the discharge lamp 10 when, for example, the useroperates the power switch (not shown) of the projector device 1.

FIG. 2 shows an example of the functional configuration of the dischargelamp lighting device 70. The discharge lamp lighting device 70 isconfigured including a down chopper section 71, the power conversionsection 72, the resonant circuit section 73, a voltage detection section74, a lighting detection section 75, and a control section 76. Amongthese constituents, the down chopper section 71 is for converting thedirect-current power, which is applied between an input terminal TIN1and an input terminal TIN2 from a direct-current power supply not shown,and has a voltage Vin, into the direct-current power having apredetermined direct-current voltage, and is composed of an n-channelfield effect transistor 711, a choke coil 712, a diode 713, and acapacitor 714. According to the down chopper section 71, by chopping thecurrent flowing through the n-channel field effect transistor 711 basedon a control signal S711 supplied from the control section 76,direct-current power having a desired output voltage corresponding tothe duty ratio of the control signal S711 is obtained. In the presentembodiment, the output voltage of the down chopper section 71 is, forexample, 380V, but the invention is not limited to this voltage value.

It should be noted that the down chopper section 71 is not necessarilyan essential constituent of the projector device 1 according to thepresent embodiment, and can therefore be eliminated.

The power conversion section 72 is for converting the direct-currentpower supplied from the down chopper section 71 into alternating-currentpower, and supplying the alternating-current power to the discharge lamp10 via the resonant circuit section 73 described later, and is composedof n-channel field effect transistors 721 through 724 forming afull-bridge circuit. Here, the respective drains of the n-channel fieldeffect transistors 721, 722 are connected to a high potential node NHconnected to the input terminal TIN1 via the n-channel field effecttransistor 711 and the choke coil 712, which constitute the down choppersection 71. The respective sources of the n-channel field effecttransistors 721, 722 are connected to the respective drains of then-channel field effect transistors 723, 724. The respective sources ofthe n-channel field effect transistors 723, 724 are connected to a lowpotential node NL connected to the input terminal TIN2 via a resistor751 constituting the lighting detection section 75 described later.

The gate of the n-channel field effect transistor 721 and the gate ofthe n-channel field effect transistor 724 are supplied with a controlsignal Sa from the control section 76, and the gate of the n-channelfield effect transistor 722 and the gate of the n-channel field effecttransistor 723 are supplied with a control signal Sb, which correspondsto an inversion signal of the control signal Sa described above, fromthe control section 76. In the present embodiment, a connection sectionbetween the source of the n-channel field effect transistor 721 and thedrain of the n-channel field effect transistor 723 is defined as oneoutput node N1 of the power conversion section 72, and a connectionsection between the source of the n-channel field effect transistor 722and the drain of the n-channel field effect transistor 724 is defined asthe other output node N2 of the power conversion section 72. It isarranged that by the pair of n-channel field effect transistors 722, 723and the pair of n-channel field effect transistors 721, 724 performingswitching in a complementary manner based on the control signals S (Sa,Sb) supplied from the control section 76, the voltages of 380V and 0Vare output from the output nodes N1, N2 in a complementary manner. Inother words, due to the switching operation of these n-channel fieldeffect transistors 721 through 724, the power conversion section 72converts the direct-current power into the alternating-current power.The alternating-current power is a rectangular wave, and has a basicfrequency fs. The frequency fs of the alternating-current powercoincides with a clock frequency of the control signals S supplied fromthe control section 76 described later. In the present embodiment, theexplanation will be presented assuming that the frequency of the controlsignals S supplied from the control section 76 and the frequency of thealternating-current power supplied from the power conversion section 72are both the “frequency fs.”

The resonant circuit section 73 functions as the igniter for generatinga high voltage exceeding the discharge starting voltage (the breakdownvoltage) of the discharge lamp 10, and is composed of two coils 731, 732magnetically coupled to each other, and a capacitor 733. Further, thedischarge lamp 10 is connected to the resonant circuit section 73 viathe output terminals TOUT1, TOUT2. Here, one end of the coil 731 isconnected to the output node N1 of the power conversion section 72, theother end of the coil 731 is connected to one end of the coil 732, andthe other end of the coil 732 is connected to the output terminal TOUT1.One electrode of the capacitor 733 is connected to a connection nodebetween the coil 731 and the coil 732, and the other electrode of thecapacitor 733 is connected to the output node N2 of the power conversionsection 72, and at the same time to the output terminal TOUT2.

In the present embodiment, an LC series resonant circuit is formed ofthe coil 731 and the capacitor 733 constituting the resonant circuitsection 73, and basically, the resonant frequency (the resonantfrequency determined by the coil 731 and the capacitor 733) of the LCseries resonant circuit appears as the natural resonant frequency fr ofthe resonant circuit section 73. In the present embodiment, the resonantfrequency fr is set to, for example, 390 kHz. Therefore, if thefrequency fs of the alternating-current power supplied from the powerconversion section 72 coincides with the resonant frequency fr of theresonant circuit section 73 to thereby set the LC series resonantcircuit composed of the coil 731 and the capacitor 733 to the resonantstate, the inter-terminal voltage V733 of the capacitor 733 becomesinfinity in principle, and thus the high voltage necessary to startdischarge of the discharge lamp 10 can be obtained using the resonantcircuit section 73. It should be noted that since a third-orderresonance mode is used in the present embodiment as described later, thefrequency fs of the alternating-current power supplied from the powerconversion section 72 when the resonant circuit section 73 gets into theresonant state is the frequency a third as high as the natural resonantfrequency fr of the resonant circuit section 73. In other words, if anN-order resonant mode is used, the frequency fs of thealternating-current power supplied from the power conversion section 72when the resonant circuit section 73 gets into the resonant statebecomes the frequency an Nth as high as the natural frequency fr of theresonant circuit section 73.

However, even if the LC resonant circuit described above gets into theresonant state, if the resistance component of the n-channel fieldeffect transistors 721 through 724 constituting the power conversionsection 72 or the wiring impedance exists, the inter-terminal voltageV733 of the capacitor 733 fails to exceed the level of about 1 through1.5 kV, and it becomes unachievable to obtain the high voltage necessaryto start discharge of the discharge lamp 10. Therefore, in the presentembodiment, the resonant circuit section 73 is provided with the coil732 magnetically connected to the coil 731 constituting the LC seriesresonant circuit, and amplifies the inter-terminal voltage V733 of thecapacitor 733 in accordance with the turn ratio between the coil 731 andthe coil 732 to thereby finally generate the high voltage of several kVnecessary to start discharge of the discharge lamp 10.

Further, in the present embodiment, the resonant circuit section 73 usesa so-called third-order resonance mode to thereby resonate at thefrequency three times as high as the frequency fs of thealternating-current power supplied from the power conversion section 72in the lighting start period. Here, the third-order resonance mode usesthe vibrational component of the waveform of the alternating-currentpower output from the power conversion section 72. In principle, thepower conversion section 72 outputs a rectangular wave as the waveformof the alternating-current power, and the waveform includes a harmoniccomponent. Using the harmonic component, the resonant circuit section 73is designed to resonate at a frequency three times as high as thefrequency fs of the alternating-current power output from the powerconversion section 72 in the lighting start period. In other words, theresonant frequency fr of the resonant circuit section 73 is set to thefrequency three times as high as the frequency fs of thealternating-current power output from the power conversion section 72 inthe lighting start period. In the present embodiment, the resonantfrequency fr of the resonant circuit section 73 is set to 390 kHz, andwhen the alternating-current power at 130 kHz is supplied from the powerconversion section 72, the resonant circuit section 73 resonates at 390kHz three times as high as the frequency due to the third-orderresonance mode. As described above, by using the third-order resonancemode, the resonant frequency fr of the resonant circuit section 73 canbe set to be relatively higher than the frequency fs of thealternating-current power described above. Therefore, it becomespossible to set each of the values of the inductance components of thecoils 731, 732 and the capacitance component of the capacitor 733constituting the resonant circuit section 73 to be smaller as comparedwith the case not using the third-order resonance mode, and thusconfigure the resonant circuit section 73 to be compact. Further, amongthe coils 731, 732 constituting the resonant circuit section 73, thecoil 732 can be eliminated. In the case in which, for example, thevoltage for lighting the discharge lamp 10 is low, or the influence ofeach of the elements and patterns is small and the inter-terminalvoltage V733 is high, the coil 732 becomes unnecessary, and thus, theresonant circuit section 73 can be configured compact.

Therefore, the resonant circuit section 73 can be configured morecompact by matching the resonant frequency fr of the resonant circuitsection 73 with the frequency (390 kHz) three times as high as thefrequency fs of the alternating-current power output from the powerconversion section 72 in the lighting start period using the third-orderresonance mode compared to the case of matching the resonant frequencyfr of the resonant circuit section 73 with the frequency fs (130 kHz) ofthe alternating-current power described above. Further, by using thethird-order resonance mode, the frequency fs of the alternating-currentpower output by the power conversion section 72 can be set to arelatively low level even if the resonant frequency fr of the resonantcircuit section 73 is set to a high level. Therefore, the switchingoperation in the high voltage region by the power conversion section 72can be stabilized, and it becomes possible to reduce the load of thepower conversion section 72.

The frequency fs of the alternating-current power described above in thecase of causing the resonance of the resonant circuit section 73 in sucha third-order resonance mode has an equivalent technical sense to thenatural resonant frequency fr of the resonant circuit section 73 interms of bringing the resonant circuit section 73 into the resonantstate, and can apparently be treated as the resonant frequency of theresonant circuit section 73. Therefore, the frequency fs of thealternating-current power of the power conversion section 72 for causingthe resonance of the resonant circuit section 73 in the third-orderresonance mode is hereinafter referred to as a “resonant frequency fsrof the resonant circuit section 73,” or simply as a “resonant frequencyfsr.” The resonant frequency fsr is stored in, for example, a storagesection not shown provided to the control section 76.

It should be noted that in the present embodiment, the third-orderresonance mode is not necessarily an essential element, and if thethird-order resonance mode is not used (i.e., in the case of using thefirst-order resonance mode), the resonant frequency fsr coincides withthe natural resonant frequency fr of the resonant circuit section 73.Further, although in the present embodiment, the case in which theresonant circuit section 73 resonates in the third-order resonance modeis cited as an example, the third-order resonance mode is not alimitation, and it is also possible to assume that the resonant circuitsection 73 resonates using an N-order resonance mode (N denotes an oddnumber). In this case, the resonant frequency fsr is defined as thefrequency at which the resonance of the resonant circuit section 73 iscaused in the arbitrary N-order resonance mode including the naturalresonant frequency fr of the resonant circuit section 73, and thefrequency of the alternating-current power supplied from the powerconversion section 72 or the frequency of the control signals S.

The voltage detection section 74 is for detecting the inter-terminalvoltage V733 of the capacitor 733 constituting the resonant circuitsection 73 described above, and is composed of resistors 741, 742connected in series between the terminals of the capacitor 733, and ananalog/digital (A/D) conversion section 743. Here, the resistors 741,742 are for dividing the inter-terminal voltage V733 of the capacitor733 of the resonant circuit section 73 to obtain a voltage V74corresponding to the resistor ratio thereof. In the present embodiment,the inter-terminal voltage V733 of the capacitor 733 is referred to as a“resonant output voltage V733.” The analog/digital conversion section743 is for converting the voltage V74 thus divided into digital data andthen outputting the digital data. In the present embodiment, the voltageV74 is a voltage of an intermediate stage generated for matching theresonant output voltage V733 with the input characteristic of theanalog/digital conversion section 743. Therefore, the digital dataoutput by the analog/digital conversion section 743 represents the valueof the resonant output voltage V733, and the resonant output voltageV733 detected by the voltage detection section 74 is supplied to thecontrol section 76.

The lighting detection section 75 is for detectinglighting/failure-in-lighting of the discharge lamp 10, and is composedof the resistor 751 and a comparator section 752. Here, the resistor 751is connected between the input terminal TIN2 and the sources of therespective n-channel field effect transistors 723, 724 constituting thepower conversion section 72, and the inter-terminal voltage (a dropvoltage) of the resistor 751 is input to the comparator section 752. Thecomparator section 752 detects the current flowing through the dischargelamp 10 based on the inter-terminal voltage of the resistor 751, and bycomparing the current thus detected and a predetermined voltage value(not shown) corresponding to the current, which flows through theresistor 751 when the discharge lamp 10 starts lighting, with eachother, lighting/failure-in-lighting of the discharge lamp 10 isdetected. Specifically, the lighting detection section 75 detectslighting of the discharge lamp 10 if, for example, the inter-terminalvoltage of the resistor 751 is equal to or higher than a predeterminedvoltage value, and detects failure-in-lighting of the discharge lamp 10if the inter-terminal voltage of the resistor 751 falls below thepredetermined voltage value. When detecting lighting of the dischargelamp, the lighting detection section 75 outputs a signal representingthe detection of lighting of the discharge lamp to the control section76.

The control section 76 is for controlling the switching operation ofeach of the down chopper section 71 and the power conversion section 72described above, and in the present embodiment, the control section 76controls the switching operation of the power conversion section 72 soas to change the frequency fs of the alternating-current power suppliedfrom the power conversion section 72 to the resonant circuit section 73in a stepwise manner with a basic frequency fo, which is different fromthe resonant frequency fsr of the resonant circuit section 73,intervening therebetween in the lighting start period until thedischarge lamp 10 reaches the stationary lighting state.

Here, the basic frequency fo is a frequency lower than the resonantfrequency fsr of the resonant circuit section 73, and is not equal tozero. In the present embodiment, it is assumed that the basic frequencyfo is 50 kHz. The lower limit value of the basic frequency fo is set tothe frequency at which a rush current from the power conversion section72 toward the lamp via the resonant circuit section 73 is not formedwhen the frequency fs of the alternating-current power supplied from thepower conversion section 72 is dropped. Further, the upper limit valueof the basic frequency fo is set to a level lower than the resonantfrequency fsr of the resonant circuit section 73, but is preferably setto the frequency at which the resonant circuit section 73 does not reachthe resonant state (the state in which the resonant output voltage V733increases). The basic frequency fo can arbitrarily be set within a rangedefined by the lower limit value and the upper limit value describedabove.

The control section 76 is provided with a voltage controlled oscillator761. The voltage controlled oscillator is for outputting the signal withthe frequency corresponding to the input voltage (not shown) as acontrol signal S. The signal defining the input voltage of the voltagecontrolled oscillator 761 is generated in the control section 76 so thatthe switching operation described later of the power conversion section72 can be obtained.

Then, the operation of the projector device 1 according to the presentembodiment will be explained focusing attention on the discharge lamplighting device 70.

FIG. 3 is an explanatory diagram for explaining an overall operation ofthe discharge lamp lighting device 70 according to the presentembodiment, and shows frequency dependency (resonant characteristics) ofthe resonant output voltage V733 of the resonant circuit section 73. Asshown in this example, the resonant output voltage V733 in the resonantcircuit section 73 shows the maximum value Vr when the frequency f ofthe harmonic wave included in the alternating-current power supplied tothe resonant circuit section 73 in the third-order resonance modecoincides with the resonant frequency fr (390 KHz) of the resonantcircuit section 73. Therefore, by setting the frequency fs of thealternating-current power of the power conversion section 72 to thefrequency at which the resonant output voltage V733 shows the maximumvalue Vr, the high voltage necessary to start the discharge of thedischarge lamp 10 can be obtained even if the resonant frequency varies.

Therefore, in the present embodiment, the control section 76 sets apredetermined frequency fd sufficiently higher than the resonantfrequency fsr of the resonant circuit section 73 to a starting point,and changes the frequency fs of the alternating-current power suppliedfrom the power conversion section 72 in a descending direction from thefrequency fd toward the resonant frequency fsr in the order offrequencies fc, fb, fa, and fx in a stepwise manner with thepredetermined basic frequency fo, which is different from the resonantfrequency fsr of the resonant circuit section 73, interveningtherebetween. Then, the control section 76 identifies the resonantfrequency fsr or a frequency adjacent thereto based on the resonantoutput voltage V733 corresponding to each of the frequencies except thebasic frequency fo. In the present embodiment, since the third-orderresonance mode is used, the frequency a third of the natural resonantfrequency fr of the resonant circuit section 73 is identified as theresonant frequency fsr.

In the present embodiment, the frequencies fa, fb, fc, fd, and fx exceptthe basic frequency fo are referred to as “drive frequencies,” and aredistinguished from the basic frequency fo. The basic frequency fo andthe drive frequencies fa, fb, fc, fd, and fx each represent thefrequency fs of the alternating-current power supplied from the powerconversion section 72, and the frequency fs of the alternating-currentpower coincides with the frequency of the control signal S supplied fromthe control section 76. Therefore, the basic frequency fo and the drivefrequencies fx, fa, fb, fc, and fd each denote the frequency of thecontrol signal S generated in the control section 76, and the frequencyfs of the alternating-current power supplied from the power conversionsection 72 is set by the control section 76 to either of the basicfrequency fo and the drive frequencies fa, fb, fc, fd, and fx. It shouldbe noted that the invention is not limited to this example, but thenumber of drive frequencies can arbitrarily be increased.

Further, the drive frequencies fa, fb, fc, fd, and fx are generated withintervals of a constant frequency step. In other words, the controlsection 76 changes (decreases) the frequency fs of thealternating-current power supplied from the power conversion section 72in a stepwise manner from the frequency fd toward the resonant frequencyfsr with the constant frequency steps. It should be noted that theinvention is not limited to this example, but the frequency steps can beset smaller in the vicinity of the resonant frequency fsr, for example.

Further, the drive frequency fd first set as the frequency fs in theprocess of changing the frequency fs of the alternating-current power ina stepwise manner is the frequency sufficiently higher than the resonantfrequency fsr as described above, and is preferably set to a valueexceeding the variation range of the resonant frequency fsr. Thus, itbecomes possible to detect the peak value Vr of the resonant outputvoltage V733 in the process of changing the frequency fs of thealternating-current power supplied from the power conversion section 72in a stepwise manner as described later even if the apparent resonantfrequency fsr varies due to the variation in the natural resonantfrequency fr of the resonant circuit section 73.

FIG. 4 is a waveform chart for supplementarily explaining the operationof the discharge lamp lighting device 70 according to the presentembodiment, and schematically shows a correspondence relationshipbetween the control signal S (the waveform shown in the upper part ofthe drawing) for providing the frequency fs of the alternating-currentpower and the waveform (the waveform shown in the lower part of thedrawing) of the resonant output voltage V733 in the resonant circuitsection 73.

As shown in the upper part of FIG. 4, the control signal S alternatelyincludes the basic frequency fo described above and the drivefrequencies (fc, fd) decreasing in a stepwise manner. In this example,the frequency fs of the control signal S is first set to the basicfrequency fo, then set to the drive frequency fd, then set to the basicfrequency fo again, and then set to the drive frequency fc. Further, asshown in the lower part of the drawing, the amplitude of the resonantoutput voltage V733 corresponding to the basic frequency fo of thecontrol signal S is decreased, and the amplitude of the resonant outputvoltage V733 corresponding to the drive frequencies (fc, fd) decreasingin a stepwise manner is increased. The amplitude values Vc, Vd of theresonant output voltage V733 on this occasion correspond to the voltagesVc, Vd at the respective drive frequencies fc, fd shown in FIG. 3described above.

As described above, in the process of decreasing the frequency fs of thealternating-current power in a stepwise manner, if lighting of thedischarge lamp 10 is not detected by the lighting detection section 75,the control section 76 decreases the frequency fs of thealternating-current power in a stepwise manner with the basic frequencyfo, which is different from the resonant frequency fsr of the resonantcircuit section 73, intervening therebetween to thereby decrease thefrequency fs of the alternating-current power until the lightingdetection section 75 detects lighting. Then, if the lighting detectionsection 75 detects lighting of the discharge lamp 10, the controlsection 76 sets the frequency fs of the alternating-current power to thepredetermined frequency of the stationary lighting state. Specifically,after the discharge of the discharge lamp 10 starts, the frequency fs ofthe alternating-current power is decreased to the predeterminedfrequency of the stationary lighting state, and lighting (the discharge)of the discharge lamp 10 is maintained.

Further, in the process of decreasing the frequency fs of thealternating-current power in a stepwise manner described above, if thefrequency fs of the alternating-current power falls below the resonantfrequency fsr while the discharge lamp 10 fails to light, and theresonant output voltage V733 detected by the voltage detection section74 exceeds the peak voltage Vr shown in FIG. 3, and the change in theresonant output voltage V733 is switched from increase to decrease, thecontrol section 76 resets the frequency fs of the alternating-currentpower to the drive frequency to which the frequency fs is set in theprevious stage. Thus, it is possible to set the frequency fs of thealternating-current power to the drive frequency adjacent to thefrequency at which the resonant output voltage V733 becomes the highest,namely the resonant frequency fsr having the highest possibility ofstarting the discharge in the process of decreasing the frequency fs ofthe alternating-current power in a stepwise manner, and the controlsection 76 waits for the start of the discharge of the discharge lamp 10in this setting state. It should be noted that if the discharge lamp 10does not start the discharge even if specified time has elapsed, anerror is output to a system control section of the projector device 1 asdescribed later.

As described above, by decreasing the frequency fs of thealternating-current power toward the resonant frequency fsr in astepwise manner with the predetermined basic frequency fo, which islower than the resonant frequency fsr of the resonant circuit section73, intervening therebetween in the lighting process instead ofcontinuously changing the frequency fs of the alternating-current powersupplied to the resonant circuit section 73, the resonant circuitsection 73 is prevented from being continuously left in thequasi-resonant state or the resonant state. Thus, since the reactancecomponent of the resonant circuit section 73 is temporarily actualizedin the section corresponding to the basic frequency fo, the voltage andthe current in the resonant circuit section 73 are suppressed, and thepower consumption in the resonant circuit section 73 is reduced. Inaddition, since the basic frequency fo included in the control signal Sis a frequency lower than the resonant frequency fsr of the resonantcircuit section 73, the frequency of the switching operation in thepower conversion section 72 for supplying the alternating-current poweris decreased. Therefore, it is possible to reduce the power consumptiondue to the switching operation in the power conversion section 72.Therefore, it becomes possible to light the discharge lamp 10 whilesuppressing the power consumption in the lighting process. Further,since the frequency of the switching operation in the power conversionsection 72 is decreased, it is also possible to stabilize the switchingoperation in the high voltage region of the power conversion section 72.

Further, in the present embodiment, since the resonant circuit section73 operates in a capacitive region in the process of changing thefrequency fs of the alternating-current power in a stepwise manner, thecurrent reversely flowing from the resonant circuit section 73 to thepower conversion section 72 in the case in which the power conversionsection 72 operates in the conductive region is prevented. Therefore, itbecomes possible to prevent the loss due to the reverse current.

Then, based on the operation of the discharge lamp lighting device 70described above, the operation of the projector device 1 according tothe present embodiment will be explained.

FIG. 5 is a flowchart showing an example of a flow of the operation ofthe projector device according to the present embodiment.

Firstly, if an operation of a power switch (not shown) is performed bythe user, the system control section (not shown) formed of the CPU 80 ofthe projector device 1 instructs the discharge lamp lighting device 70to light the discharge lamp 10.

When receiving the instruction from the system control section describedabove, the control section 76 of the discharge lamp lighting device 70starts the switching operation of the down chopper section 71 with thecontrol signal S711, and at the same time, sets (step S1) the basicfrequency fo described above as the frequency fs of the control signalS, and then starts the switching operation of the power conversionsection 72 with the control signal S.

Subsequently, the control section 76 determines (step S2) whether or notthe resonant frequency fsr (the frequency fs of the alternating-currentpower applied to the resonant circuit section 73 corresponding to theresonant frequency fr, namely the frequency of the signal S) describedabove is stored in a storage section not shown provided to the controlsection 76. Here, in the present embodiment, if the lighting operationhas ever been performed in the past, the drive frequency at which thedischarge of the discharge lamp 10 has started is stored in the storagesection as the resonant frequency fsr due to the step S9 described laterin the past lighting operation. If the resonant frequency fsr is storedin the storage section (YES in the step S2), the control section 76 sets(step S3) the drive frequency in accordance with the resonant frequencyfsr thus stored. Here, it is assumed that the lighting operation has notever been performed in the past, and the resonant frequency fsr of thepast lighting operation is not stored in the storage section not shownprovided to the control section 76 (NO in the step S2).

If the resonant frequency fsr of the past lighting operation is notstored in the storage section (NO in the step S2), the control section76 sets (step S4) the predetermined drive frequency fd as the frequencyfs of the control signal S. It should be noted that if the resonantfrequency fsr is stored in the storage section, the drive frequency isset in accordance with the resonant frequency fsr in the step S3, and ifthe drive frequency is, for example, the frequency fd, the flow of theoperation on and after the step S5 described later will be performed.The power conversion section 72 performs the switching operation basedon the control signal S having the drive frequency fd, and supplies theresonant circuit section 73 with the alternating-current power havingthe drive frequency fd. In the section corresponding to the controlsignal S with the drive frequency fd, the voltage detection section 74detects (step S5) the resonant output voltage V733. The control section76 temporarily stores (step S6) the resonant output voltage V733detected by the voltage detection section 74 into the storage sectionnot shown.

Then, the control section 76 resets (step S7) the basic frequency fo tothe frequency fs of the control signal S. In the section of the controlsignal S with the basic frequency fo, the control section 76 determines(step S8) whether or not the resonant output voltage V733 thus detectedis equal to or higher than the resonant output voltage V733 detectedpreviously. Here, since the resonant output voltage V733 is the voltageobtained corresponding to the first drive frequency fd, no previousvalue exists. In this case, the control section 76 determines that it isequal to or higher than the resonant output voltage V733 detectedpreviously (YES in the step S8). The determination process is forfiguring out whether or not the frequency fs of the control signal Sexceeds the resonant frequency fsr shown in FIG. 3. If the resonantoutput voltage V733 thus detected is lower than the previous one (NO inthe step S8), the control section 76 stores (step S9) the previous drivefrequency, here the frequency fd, into the storage section of thecontrol section 76 as the resonant frequency.

Further, in the case in which the discharge lamp 10 does not light inthe step S11 (NO in the step S11), and in the case in which thespecified operation time period has elapsed in the step S13 (YES in thestep S13), the control section 76 outputs a lamp failure-in-lightingerror to the system control section of the projector device 1, and then,the user is notified of the fact that the lamp failure-in-lighting erroroccurs via a display section or the like not shown under the control ofthe system control section. On this occasion, the system control sectionof the projector device 1 performs a predetermined process for resolvingthe error such as operating a fan for cooling the discharge lamp 10.Further, it becomes possible for the user receiving the notification toperform a response such as postponing the use of the projector device 1for a certain period of time.

It should be noted that the basic frequency fo in the step S7 describedabove and the basic frequency fo in the step S10 are not required to bethe same as each other, and can be different from each other providingthe frequencies are lower than the resonant frequency, namely 50 kHz and60 Hz, for example. Further, the specified operation time periods in thestep S13 and the step S17 are not required to be the same specifiedoperation time period, but can be different from each other.

Subsequently, the control section 76 sets (step S10) the basic frequencyfo again to the frequency fs of the control signal S. In the section ofthe control signal S with the basic frequency fo, the control section 76determines (step S11) whether or not the discharge lamp 10 startslighting based on the detection result of the lighting detection section75. Here, if it is determined that the discharge lamp 10 does not light(No in the step S11), the control section 76 measures (step S12) theoperation time period having elapsed from the start of the lightingoperation, and then determines (step S13) whether or not the specifiedoperation time period has elapsed. Here, if the specified operation timeperiod has not elapsed (NO in the step S13), the control section 76drops the frequency fs of the control signal S and then sets (step S14)the drive frequency fc. Subsequently, the control section 76 returns theprocessing operation to the step S1 described above, and then repeatedlyperforms substantially the same steps until it is determined in the stepS11 described above that the discharge lamp 10 starts lighting.

Here, if it is determined in the step S11 described above that thedischarge lamp 10 starts lighting (YES in the step S11) in the case inwhich the clock frequency of the control signal S is set to thefrequency fc in the step S14, the control section 76 sets (step S15) thefrequency fs of the control signal S to the basic frequency fo, and thenmeasures (step S16) the specified operation time period. Then, thecontrol section 76 determines (step S17) whether or not the specifiedoperation time period has elapsed. If the specified operation timeperiod has not elapsed (NO in the step S17), the control section 76repeats the steps S11 through S17 until the specified operation timeperiod elapses. If the specified operation time period has elapsed (YESin the step S17), the control section 76 sets the predeterminedfrequency in the normal lighting state as the frequency fs of thecontrol signal S, and then outputs (step S18) the normal lamp lightingsignal waveform as the control signal S.

Further, in the case in which the discharge lamp 10 does not light inthe step S11 (NO in the step S11), and in the case in which thespecified operation time period has elapsed in the step S13 (YES in thestep S13), the control section 76 outputs a lamp failure-in-lightingerror to the system control section of the projector device 1, and then,the user is notified of the fact that the lamp failure-in-lighting erroroccurs via a display section or the like not shown under the control ofthe system control section. On this occasion, the system control sectionof the projector device 1 performs a predetermined process for resolvingthe error such as operating the fan for cooling the discharge lamp 10.Further, it becomes possible for the user receiving the notification toperform a response such as postponing the use of the projector device 1for a certain period of time.

It should be noted that although it is assumed in the embodimentdescribed above that the discharge lamp lighting device 70 is aconstituent of the projector device 1, it is also possible to configurethe discharge lamp lighting device 70 as a separate device from theprojector device 1.

Further, it is also possible to express the operation procedure of thedischarge lamp lighting device 70 according to the embodiment describedabove as a discharge lamp lighting method. The discharge lamp lightingmethod can be expressed as a method including a step of converting thedirect-current power into the alternating-current power by the powerconversion section 72, and then supplying the discharge lamp 10 with thealternating-current power via the resonant circuit section 73, and astep of changing the frequency fs of the alternating-current powerdescribed above by the control section 76 in a stepwise manner with thebasic frequency fo, which is different from the frequency fr causing theresonance of the resonant circuit section 73, intervening therebetweenin the lighting start period until the discharge lamp 10 reaches thestationary lighting state.

Although the embodiment of the invention is hereinabove explained, theinvention is not limited to the embodiment described above, but canvariously be modified within the scope or the spirit of the invention.

For example, although in the embodiment described above the powerconversion section 72 is configured using the full-bridge circuit, it isalso possible to use an arbitrary circuit configuration such as ahalf-bridge as the circuit configuration of the power conversion section72 providing the alternating-current power can be supplied to theresonant circuit section 73.

Further, the circuit configurations of the voltage detection section 74and the lighting detection section 75 are not limited to the embodimentdescribed above, but arbitrary circuit configurations can be used.

Second Embodiment

Hereinafter, a second embodiment out of some aspects of embodying theinvention will be explained in detail with reference to the accompanyingdrawings.

In comparison between a discharge lamp lighting device 70 a according tothe present embodiment and the discharge lamp lighting device 70according to the first embodiment, there is a difference in the pointthat a current detection section 74 a, a lighting detection section 75a, and a control section 76 a are provided instead of the voltagedetection section 74, the lighting detection section 75, and the controlsection 76. The functional configuration is substantially the sameexcept the point, and therefore, the explanation therefor will beomitted.

FIG. 6 shows an example of the functional configuration of the dischargelamp lighting device 70 a. The discharge lamp lighting device 70 a isconfigured including the down chopper section 71, the power conversionsection 72, the resonant circuit section 73, the current detectionsection 74 a, the lighting detection section 75 a, and the controlsection 76 a.

The current detection section 74 a is for detecting a current I733flowing through the capacitor 733 constituting the resonant circuitsection 73 described above, and is formed of a resistor 741 a connectedin series to one end of the capacitor 733. Here, the resistor 741 a isfor obtaining the current I733 flowing through the capacitor 733 of theresonant circuit section 73 based on the potential difference thereof.In the present embodiment, the current I733 flowing through thecapacitor 733 is referred to as a “resonant output current I733.” Thecurrent detection section 74 a performs the analog/digital conversion onthe resonant output current I733, the digital data represents the valueof the resonant output current I733, and the resonant output currentI733 detected by the current detection section 74 a is supplied to thecontrol section 76 a. It should be noted that the current detectionsection 74 a always monitors the resonant output current I733, and if anabnormal current such as an excessive current is detected, the currentdetection section 74 a notifies the control section 76 a of the resonantoutput current I733 thus detected, and the control section 76 a stopsthe control on the ground of an error.

It should be noted that although in the present embodiment the resonantoutput current I733 is detected using the resistor 741 a, it is alsopossible to detect the resonant output current I733 using a resistor 751a of the lighting detection section 75 a described later. In this case,the current detection section 74 a becomes unnecessary, and the circuitcan be downsized.

The lighting detection section 75 a is for detectinglighting/failure-in-lighting of the discharge lamp 10, and is composedof the resistor 751 a and a comparator section 752 a. Here, the resistor751 a is connected between a connection node of the input terminal TIN2and the diode 713 of the down chopper section 71, and a connection nodeof the capacitor 714 of the down chopper section 71 and the sources ofthe respective n-channel field effect transistors 723, 724 constitutingthe power conversion section 72, and the inter-terminal voltage (a dropvoltage) of the resistor 751 a is input to the comparator section 752 a.The comparator section 752 a detects the current flowing through thedischarge lamp 10 based on the inter-terminal voltage of the resistor751 a, and by comparing the current thus detected and the current, whichflows through the resistor 751 a when the discharge lamp 10 startslighting, with each other, lighting/failure-in-lighting of the dischargelamp 10 is detected. Specifically, the lighting detection section 75 adetects lighting of the discharge lamp 10 if, for example, theinter-terminal current of the resistor 751 a is equal to or higher thana predetermined current value, and detects failure-in-lighting of thedischarge lamp 10 if the inter-terminal current of the resistor 751 afalls below the predetermined current value. When detecting lighting ofthe discharge lamp, the lighting detection section 75 a outputs a signalrepresenting the detection of lighting of the discharge lamp to thecontrol section 76 a.

Although the current value is input to the control section 76 a insteadof the voltage value, the control section 76 a performs substantiallythe same operation as that of the control section 76 in the firstembodiment. The control section 76 a is provided with a currentcontrolled oscillator 761 a. The current controlled oscillator 761 a isfor outputting the signal with the frequency corresponding to the inputcurrent (not shown) as the control signal S. The signal defining theinput current of the current controlled oscillator 761 a is generated inthe control section 76 a so that the switching operation described laterof the power conversion section 72 can be obtained.

FIG. 7 is an explanatory diagram for explaining an overall operation ofthe discharge lamp lighting device 70 a provided to the projector device1 a according to the present embodiment.

FIG. 7 is the explanatory diagram of the case in which the currentdetection section 74 a performs the resonant output current detectioninstead of the voltage detection section 74 detecting the resonantoutput voltage in FIG. 3, and therefore, the explanation therefor willbe omitted.

FIG. 8 is a waveform chart for supplementarily explaining an overalloperation of the discharge lamp lighting device 70 a provided to theprojector device 1 a according to the present embodiment.

As shown in the upper part of FIG. 8, the control signal S alternatelyincludes the basic frequency fo described above and the drivefrequencies (fc, fd) decreasing in a stepwise manner. In this example,the frequency fs of the control signal S is first set to the basicfrequency fo, then set to the drive frequency fd, then set to the basicfrequency fo again, and then set to the drive frequency fc. Further, asshown in the lower part of the drawing, the amplitude of the resonantoutput current I733 corresponding to the basic frequency fo of thecontrol signal S is decreased, and the amplitude of the resonant outputcurrent I733 corresponding to the drive frequencies (fc, fd) decreasingin a stepwise manner is increased. The amplitude values Ic, Id of theresonant output current I733 on this occasion correspond to the currentsIc, Id at the respective drive frequencies fc, fd shown in FIG. 7described above.

As described above, in the process of decreasing the frequency fs of thealternating-current power in a stepwise manner, if lighting of thedischarge lamp 10 is not detected by the lighting detection section 75a, the control section 76 a decreases the frequency fs of thealternating-current power in a stepwise manner with the basic frequencyfo, which is different from the resonant frequency fsr of the resonantcircuit section 73, intervening therebetween to thereby decrease thefrequency fs of the alternating-current power until the lightingdetection section 75 a detects lighting. Then, if the lighting detectionsection 75 a detects lighting of the discharge lamp 10, the controlsection 76 a sets the frequency fs of the alternating-current power tothe predetermined frequency of the stationary lighting state.Specifically, after the discharge of the discharge lamp 10 starts, thefrequency fs of the alternating-current power is decreased to thepredetermined frequency of the stationary lighting state, and lighting(the discharge) of the discharge lamp 10 is maintained.

Further, in the process of decreasing the frequency fs of thealternating-current power in a stepwise manner described above, if thefrequency fs of the alternating-current power falls below the resonantfrequency fsr while the discharge lamp 10 fails to light, and theresonant output current I733 detected by the current detection section74 a exceeds the peak current Ir shown in FIG. 7, and the change in theresonant output current I733 is switched from increase to decrease, thecontrol section 76 a resets the frequency fs of the alternating-currentpower to the drive frequency to which the frequency fs is set in theprevious stage. Thus, it is possible to set the frequency fs of thealternating-current power to the drive frequency adjacent to thefrequency at which the resonant output current I733 becomes the highest,namely the resonant frequency fsr having the highest possibility ofstarting the discharge in the process of decreasing the frequency fs ofthe alternating-current power in a stepwise manner, and the controlsection 76 a waits for the start of the discharge of the discharge lamp10 in this setting state. It should be noted that if the discharge lamp10 does not start the discharge even if specified time has elapsed, anerror is output to the system control section of the projector device 1a as described later.

FIG. 9 is a flowchart showing an example of a flow of the operation ofthe projector device 1 a according to the present embodiment. FIG. 9 issufficiently described by reading “voltage” in the flowchartrepresenting the example of the flow of the operation of the projectordevice 1 shown in FIG. 5 with “current,” and therefore, the explanationtherefor will be omitted.

As described above, according to the present embodiment, substantiallythe same advantages as in the first embodiment can be obtained.

Third Embodiment

Hereinafter, a third embodiment out of some aspects of embodying theinvention will be explained in detail with reference to the accompanyingdrawings.

In comparison between the discharge lamp lighting device 70 a accordingto the present embodiment and the discharge lamp lighting device 70 aaccording to the second embodiment, the functional configuration issubstantially the same, and therefore, the explanation therefor will beomitted. It should be noted that the setting method of the drivefrequency is different, and will therefore be explained.

FIG. 11 is a diagram showing an example of transition of drive frequencysetting time periods IMPT1, IMPT2 and lighting detection time periodsDETT1, DETT2 according to the present embodiment.

The control section 76 a performs the detection of the drive frequencyadjacent to the resonant frequency fsr in the drive frequency settingtime periods IMPT1, IMPT2. Since the drive frequency setting timeperiods IMPT1, IMPT2 are the time periods for performing substantiallythe same processes, and are therefore collectively referred to as thedrive frequency setting time period IMPT in the following explanation.The drive frequency setting time period IMPT is, for example, 1000 ms.The control section 76 a applies the frequency detected in the drivefrequency setting time period IMPT to the discharge lamp 10. Thedetailed setting method of the drive frequency in the vicinity of theresonant frequency fsr will be described later. Since the lightingdetection time periods DETT1, DETT2 are the time periods for performingsubstantially the same processes, and are therefore collectivelyreferred to as the lighting detection time period DETT in the followingexplanation. The lighting detection section 75 a detects whether or notthe discharge lamp 10 is in the lighting state in the lighting detectiontime period DETT. The lighting detection time period DETT is, forexample, 500 ms. It should be noted that if the lighting detectionsection 75 a detects the fact that the discharge lamp 10 is in thelighting state in the lighting detection time period DETT1, it is notrequired to perform the detection of the drive frequency in the vicinityof the resonant frequency fsr in the drive frequency setting time periodIMPT2 by the control section 76 a, and the detection of whether or notthe discharge lamp 10 is in the lighting state in the lighting detectiontime period DETT2 by the lighting detection section 75 a.

FIG. 12 is a diagram showing an example of the transition of the drivefrequency in the drive frequency setting time period IMPT according tothe present embodiment. The explanation will be presented using theresonant characteristics of the resonant output current I733 shown inFIG. 7. The control section 76 a changes the frequency fs of thealternating-current power supplied from the power conversion section 72in a descending direction from the drive frequency fd toward theresonant frequency fsr in a stepwise manner in the order of the drivefrequencies fc, fb, fa, and fx with the predetermined basic frequencyfo, which is different from the resonant frequency fsr, interveningtherebetween. On this occasion, the control section 76 a monitors theresonant output current I733, and identifies the drive frequencyadjacent to the resonant frequency fsr based on the resonant outputcurrent I733 during the period of supplying the alternating-currentpower with each of the drive frequencies.

Specifically, the control section 76 a firstly applies the predetermineddrive frequency fd sufficiently higher than the resonant frequency fsrfor a predetermined time period T1, namely until 2 ms is reached, forexample. Subsequently, the control section 76 a applies the basicfrequency fo for a predetermined time period T2, namely until 6 ms isreached, for example. Subsequently, the control section 76 a applies thedrive frequency fc, which is the drive frequency obtained by decreasingthe drive frequency fd toward the resonant frequency fsr, until thepredetermined time period T1 is reached. Subsequently, the controlsection 76 a applies the basic frequency fo again until thepredetermined time period T2 is reached. In such a manner as describedabove, the control section 76 a identifies the drive frequency, at whichthe resonant output current I733 corresponding to each of the drivefrequencies except the basic frequency fo takes the maximum value, asthe drive frequency adjacent to the resonant frequency fsr. The controlsection 76 a repeats the application of the drive frequency adjacent tothe resonant frequency fsr thus detected and the application of thebasic frequency fo until the drive frequency setting time period IMPTshown in FIG. 12 ends. The control section 76 a alternately applies thepredetermined frequency (the drive frequency) higher than the basicfrequency fo and the frequency (the basic frequency fo) lower than thedrive frequency to thereby make the current easy to flow through thecircuit, and in the case in which the discharge lamp 10 starts lightingat the predetermined frequency (the resonant frequency) higher than thebasic frequency fo, the lighting state can be made brighter.

The control section 76 a applies the basic frequency fo in the lightingdetection time period DETT. During the period, the lighting detectionsection 75 a detects whether or not the discharge lamp 10 is in thelighting state. If the lighting detection section 75 a fails to detectthe lighting state of the discharge lamp 10, the control section 76 aperforms substantially the same process as in the drive frequencysetting time period IMPT1 again in the drive frequency setting timeperiod IMPT2. Subsequently, the control section 76 a applies the basicfrequency fo in the lighting detection time period DETT2. On thisoccasion, the lighting detection section 75 a detects again whether ornot the discharge lamp 10 is in the lighting state. If the lightingstate of the discharge lamp 10 is not detected by the lighting detectionsection 75 a, the control section 76 a gives notice of an error.

It should be noted that the predetermined time period T1 for applyingthe basic frequency fo and the predetermined time period T2 for applyingthe drive frequency are different from each other in the drive frequencysetting time period IMPT, and it is preferable that the predeterminedtime period T1 for applying the basic frequency fo is set to be longerthan the predetermined time period T2 for applying the drive frequency.Further, it is also possible to change the drive frequency with afrequency step corresponding to the detection value of the resonantoutput current I733 looking up the table Ta1 shown in FIG. 10 whenchanging the drive frequency toward the resonant frequency fsr.Specifically, the table Ta1 includes item columns of the current valueand the skip count, and the skip count, namely the number of steps of acertain frequency, is made to correspond to each of the current values.If the current value is Id, the skip count is 5, and if the currentvalue is Ic, the skip count is 4. Further, it is also possible for thecontrol section 76 a to determine the skip count using the peak value Irof the resonant output current I733 stored in advance in the storagesection, and a threshold value corresponding to the peak value Ir. Inthis case, if the current value comes closer to the peak value Ir of theresonant output current I733, namely the current value is equal to orhigher than the threshold value, the control section 76 a decreases theskip count, or changes the drive frequency in a step-by-step manner.Thus, the control section 76 a can detect the resonant frequency fasterthan in the case of changing the drive frequency in a step-by-stepmanner.

FIG. 13 is a flowchart showing an example of a flow of the operation ofthe projector device according to the present embodiment.

Firstly, if an operation of a power switch (not shown) is performed bythe user, the CPU 80 of the projector device 1 instructs the dischargelamp lighting device 70 a to light the discharge lamp 10.

When receiving the instruction described above, the control section 76 aof the discharge lamp lighting device 70 a starts the switchingoperation of the down chopper section 71 with the control signal S711,and at the same time, sets (step S1) the basic frequency fo describedabove as the frequency fs of the control signal S, and then starts theswitching operation of the power conversion section 72 with the controlsignal S.

Subsequently, the control section 76 a determines (step S2) whether ornot the resonant frequency fsr (the frequency fs of thealternating-current power applied to the resonant circuit section 73corresponding to the resonant frequency fr, namely the frequency of thesignal S) described above is stored in a storage section not shownprovided to the control section 76 a. Here, in the present embodiment,if the lighting operation has ever been performed in the past, the drivefrequency at which the discharge of the discharge lamp 10 has started inthe past lighting operation is stored in the storage section as theresonant frequency fsr. If the resonant frequency fsr is stored in thestorage section (YES in the step S2), the control section 76 a sets(step S3) the drive frequency in accordance with the resonant frequencyfsr thus stored. Here, it is assumed that the lighting operation has notever been performed in the past, and the resonant frequency fsr of thepast lighting operation is not stored in the storage section not shownprovided to the control section 76 a (NO in the step S2).

If the resonant frequency fsr of the past lighting operation is notstored in the storage section (NO in the step S2), the control section76 a sets (step S4) the predetermined drive frequency fd as thefrequency fs of the control signal S. The power conversion section 72performs the switching operation based on the control signal S havingthe drive frequency fd, and supplies the resonant circuit section 73with the alternating-current power having the drive frequency fd for thepredetermined time period T1. In the predetermined time period T1, thecurrent detection section 74 a detects the resonant output current I733(step S5 a). The control section 76 a temporarily stores (step S6 a) theresonant output current I733 detected by the current detection section74 a into the storage section not shown.

Then, the control section 76 a resets (step S7) the basic frequency foto the frequency fs of the control signal S, and then the powerconversion section 72 supplies the resonant circuit section 73 with thealternating-current power having the basic frequency fo for thepredetermined time period T2 in accordance with the setting. The controlsection 76 a determines (step S20) whether or not the resonant outputcurrent I733 temporarily stored in the step S6 a is equal to or higherthan the resonant output current I733 temporarily stored at the lasttime (in the step S6 a at the previous time). If it is determined thatthe resonant output current I733 temporarily stored in the step S6 a isequal to or higher than the resonant output current I733 detected at thelast time (YES in the step S20), the control section 76 a drops thedrive frequency by one step (step S21). It should be noted that theresonant output current I733 is the current obtained corresponding tothe first drive frequency fd, and if the last value does not exist, thecontrol section 76 a determines that the resonant output current isequal to or higher than the resonant output current I733 temporarilystored at the last time (YES in the step S20). The determination processis for figuring out whether or not the frequency fs exceeds the resonantfrequency fsr. If the resonant output current I733 is lower than theresonant output current I733 temporarily stored at the last time (NO inthe step S20), the control section 76 a sets (step S22) the drivefrequency at the last time (at the previous time) as the resonantfrequency.

Subsequently, the control section 76 a determines (step S24) whether ornot the specified time has elapsed, namely whether or not the drivefrequency setting time period IMPT ends. If the specified time has notelapsed (NO in the step S24), the process returns to the step S1. On theother hand, if the specified time has elapsed (YES in the step S24), thecontrol section 76 a sets (step S10) the basic frequency fo again as thefrequency fs. The control section 76 a determines (step S11) whether ornot the discharge lamp 10 starts lighting based on the detection resultof the lighting detection section 75 a. Here, if it is determined thatthe discharge lamp 10 does not light (No in the step S11), the controlsection 76 a measures (step S12) the operation time period havingelapsed from the start of the lighting detection, and then determines(step S25) whether or not the specified operation time period haselapsed, namely whether or not the lighting detection time period DETThas ended. Here, if the specified operation time period has not elapsed(NO in the step S25), the control section 76 a returns to the step S11.

Here, if it is determined in the step S11 that the discharge lamp 10 hasstarted lighting (YES in the step S11), the control section 76 ameasures (step S16) the specified operation time period. Then, thecontrol section 76 a determines (step S17) whether or not the specifiedoperation time period has elapsed, namely whether or not the lightingdetection time period DETT has ended. If the specified operation timeperiod has not elapsed (NO in the step S17), the process returns to thestep S11. If the specified operation time period has elapsed (YES in thestep S17), the control section 76 a sets the predetermined frequency inthe normal lighting state as the frequency fs, and then sets (step S18)the control signal S to the normal lamp lighting signal.

Further, in the case in which the discharge lamp 10 does not light inthe step S11 described above (NO in the step S11), and the specifiedoperation time period has elapsed in the step S25 described above (YESin the step S25), the control section 76 a determines (step S26) whetheror not the number of times of elapse of the specified time with thedischarge lamp 10 kept in the non-lighting state is one. If the numberis one (YES in the step S26), the process returns to the step S1. On theother hand, if the number is not one (NO in the step S26), the controlsection 76 a outputs (step S19) a failure-in-lighting error of thedischarge lamp 10 to the system control section of the projector device1, and then, the user is notified of the fact that the lampfailure-in-lighting error occurs via a display section or the like notshown under the control of the system control section. On this occasion,the system control section of the projector device 1 performs apredetermined process for resolving the error such as operating the fanfor cooling the discharge lamp 10. Further, it becomes possible for theuser receiving the notification to perform a response such as postponingthe use of the projector device 1 for a certain period of time.

It should be noted that the basic frequency fo in the step S7 describedabove, the basic frequency fo in the step S10, and the basic frequencyfo in the step S15 are not required to be the same as each other, andcan be different from each other providing the frequencies are lowerthan the resonant frequency and different from the resonant frequency,such as 50 kHz, 60 kHz, and 70 kHz, respectively. Further, the specifiedoperation time periods in the step S25 and the step S17 are not requiredto be the same specified operation time period, but can be differentfrom each other. Further, if the discharge lamp 10 is in the lightingstate in the step S11 described above, it is also possible to performthe step S18 as a subsequent operation. Further, although the resonantoutput current is detected using the current detection section 74 a tothereby determine the drive frequency in the present embodiment, it isalso possible to detect the resonant output voltage using the voltagedetection section 74 instead of the current detection section 74 a tothereby determine the drive frequency.

It should be noted that although it is assumed in the embodimentdescribed above that the discharge lamp lighting device 70 a is aconstituent of the projector device 1, it is also possible to configurethe discharge lamp lighting device 70 a as a separate device from theprojector device 1.

Further, it is also possible to express the operation procedure of thedischarge lamp lighting device 70 a according to the embodimentdescribed above as a discharge lamp lighting method. The discharge lamplighting method can be expressed as a method including a step ofconverting the direct-current power into the alternating-current powerby the power conversion section 72, and then supplying the dischargelamp 10 with the alternating-current power via the resonant circuitsection 73, and a step of changing the frequency fs of thealternating-current power described above by the control section 76 a ina stepwise manner with the basic frequency fo, which is different fromthe frequency fr causing the resonance of the resonant circuit section73, intervening therebetween in the lighting start period until thedischarge lamp 10 reaches the stationary lighting state.

Although the embodiments of the invention are hereinabove explained, theinvention is not limited to the embodiments described above, but canvariously be modified within the scope or the spirit of the invention.

For example, although in the embodiment described above the powerconversion section 72 is configured using the full-bridge circuit, it isalso possible to use an arbitrary circuit configuration such as ahalf-bridge as the circuit configuration of the power conversion section72 providing the alternating-current power can be supplied to theresonant circuit section 73.

Further, the circuit configurations of the current detection section 74a and the lighting detection section 75 a are not limited to theembodiments described above, but arbitrary circuit configurations can beused.

The entire disclosure of Japanese Patent Application Nos. 2012-64501,filed Mar. 21, 2012 and 2012-272206, filed Dec. 13, 2012 are expresslyincorporated by reference herein.

What is claimed is:
 1. A discharge lamp lighting device comprising: aresonant circuit section connected to a discharge lamp; a powerconversion section adapted to convert direct-current power intoalternating-current power and supply the discharge lamp with thealternating-current power via the resonant circuit section; a controlsection adapted to change a frequency of the alternating-current powerin a stepwise manner with a frequency, which is different from afrequency causing a resonance of the resonant circuit section,intervening between frequency values of the frequency changed in alighting start period until the discharge lamp reaches a stationarylighting state; and a lighting detection section adapted to detectlighting of the discharge lamp, wherein the control section changes thefrequency of the alternating-current power in the stepwise manner withthe frequency, which is different from the frequency causing theresonance of the resonant circuit section, intervening between thefrequency values of the frequency changed if lighting of the dischargelamp fails to be detected by the lighting detection section.
 2. Thedischarge lamp lighting device according to claim 1, wherein the controlsection changes the frequency of the alternating-current power in thestepwise manner in a descending direction toward the frequency causingthe resonance of the resonant circuit section.
 3. The discharge lamplighting device according to claim 1, wherein the frequency differentfrom the frequency causing the resonance of the resonant circuit sectionis a frequency lower than the frequency causing the resonance of theresonant circuit section.
 4. The discharge lamp lighting deviceaccording to claim 1, wherein the control section sets the frequency ofthe alternating-current power to a predetermined frequency in thestationary lighting state if the lighting detection section detectslighting of the discharge lamp.
 5. The discharge lamp lighting deviceaccording to claim 1, wherein the control section sets the frequency ofthe alternating-current power in a first time period so that thefrequency of the alternating-current power changes in the stepwisemanner with the frequency, which is different from the frequency causingthe resonance of the resonant circuit section, intervening betweenfrequency values of the frequency changing, and the lighting detectionsection detects lighting of the discharge lamp in a second time periodafter the first time period.
 6. The discharge lamp lighting deviceaccording to claim 1, further comprising: a voltage detection sectionadapted to detect a resonant output voltage of the resonant circuitsection, wherein if a change in the resonant voltage detected by thevoltage detection section is switched from increase to decrease in aprocess of changing the frequency of the alternating-current power inthe stepwise manner, the control section sets the frequency of thealternating-current power to the frequency in a previous step.
 7. Thedischarge lamp lighting device according to claim 1, further comprising:a current detection section adapted to detect a resonant output currentof the resonant circuit section, wherein if a change in the resonantcurrent detected by the current detection section is switched fromincrease to decrease in a process of changing the frequency of thealternating-current power in the stepwise manner, the control sectionsets the frequency of the alternating-current power to the frequency ina previous step.
 8. The discharge lamp lighting device according toclaim 1, further comprising: a detection section adapted to detect oneof a resonant output current and a resonant output voltage of theresonant circuit section, wherein if a change in one of the resonantcurrent and the resonant voltage detected by the detection section isswitched from increase to decrease in a first time period in a processof changing the frequency of the alternating-current power in thestepwise manner, the control section sets the frequency of thealternating-current power to the frequency in a previous step, and thelighting detection section detects lighting of the discharge lamp in asecond time period after the first time period.
 9. The discharge lamplighting device according to claim 8, wherein in the first time period,the control section applies the frequency in the previous step set asthe frequency of the alternating-current power a predetermined number oftimes before the first time period ends.
 10. The discharge lamp lightingdevice according to claim 1, wherein alternating-current power with afrequency 1/N (N denotes an integer) of the frequency of thealternating-current power is applied to the resonant circuit section.11. A discharge lamp lighting device adapted to supply a discharge lampwith alternating-current power via a resonant circuit section to therebystart discharge of the discharge lamp to light the discharge lamp, thedischarge lamp lighting device comprising: a control section adapted tochange a frequency of the alternating-current power in a stepwise mannerwith a frequency, which is different from a frequency causing aresonance of the resonant circuit section, intervening between frequencyvalues of the frequency changed in a lighting start period until thedischarge lamp reaches a stationary lighting state; and a lightingdetection section adapted to detect lighting of the discharge lamp,wherein the control section changes the frequency of thealternating-current power in the stepwise manner with the frequency,which is different from the frequency causing the resonance of theresonant circuit section, intervening between the frequency values ofthe frequency changed if lighting of the discharge lamp fails to bedetected by the lighting detection section.
 12. The discharge lamplighting device according to claim 1, wherein the frequency differentfrom the frequency causing the resonance of the resonant circuit sectionis lower than the frequency causing the resonance of the resonantcircuit section, and higher than a frequency at which a current suppliedfrom the power conversion section adapted to supply thealternating-current power is one of equal to and lower than apredetermined value.
 13. The discharge lamp lighting device according toclaim 11, wherein the frequency different from the frequency causing theresonance of the resonant circuit section is lower than the frequencycausing the resonance of the resonant circuit section, and higher than afrequency at which a current supplied from a power conversion sectionadapted to supply the alternating-current power is one of equal to andlower than a predetermined value.
 14. A discharge lamp lighting methodcomprising: converting, by a power conversion section, direct-currentpower into alternating-current power and supplying a discharge lamp withthe alternating-current power via a resonant circuit section; changing,by a control section, a frequency of the alternating-current power in astepwise manner with a frequency, which is different from a frequencycausing a resonance of the resonant circuit section, intervening betweenfrequency values of the frequency changed in a lighting start perioduntil the discharge lamp reaches a stationary lighting state; anddetecting, by a lighting detection section, the lighting of thedischarge lamp, wherein the control section changes the frequency of thealternating-current power in the stepwise manner with the frequency,which is different from the frequency causing the resonance of theresonant circuit section, intervening between the frequency values ofthe frequency changed if lighting of the discharge lamp fails to bedetected by the lighting detection section.
 15. A projector devicecomprising: the discharge lamp as a light source; and the discharge lamplighting device according to claim 1 as a device adapted to light thedischarge lamp.
 16. A projector device comprising: the discharge lamp asa light source; and the discharge lamp lighting device according toclaim 11 as a device adapted to light the discharge lamp.
 17. Adischarge lamp lighting device comprising: a resonant circuit sectionconnected to a discharge lamp; a power conversion section adapted toconvert direct-current power into alternating-current power and supplythe discharge lamp with the alternating-current power via the resonantcircuit section; a control section adapted to change a frequency of thealternating-current power in a stepwise manner with a frequency, whichis different from a frequency causing a resonance of the resonantcircuit section, intervening between frequency values of the frequencychanged in a lighting start period until the discharge lamp reaches astationary lighting state; and a voltage detection section adapted todetect a resonant output voltage of the resonant circuit section,wherein if a change in the resonant voltage detected by the voltagedetection section is switched from increase to decrease in a process ofchanging the frequency of the alternating-current power in the stepwisemanner, the control section sets the frequency of thealternating-current power to the frequency in a previous step.
 18. Adischarge lamp lighting device comprising: a resonant circuit sectionconnected to a discharge lamp; a power conversion section adapted toconvert direct-current power into alternating-current power and supplythe discharge lamp with the alternating-current power via the resonantcircuit section; a control section adapted to change a frequency of thealternating-current power in a stepwise manner with a frequency, whichis different from a frequency causing a resonance of the resonantcircuit section, intervening between frequency values of the frequencychanged in a lighting start period until the discharge lamp reaches astationary lighting state; and a current detection section adapted todetect a resonant output current of the resonant circuit section,wherein if a change in the resonant current detected by the currentdetection section is switched from increase to decrease in a process ofchanging the frequency of the alternating-current power in the stepwisemanner, the control section sets the frequency of thealternating-current power to the frequency in a previous step.
 19. Adischarge lamp lighting device comprising: a resonant circuit sectionconnected to a discharge lamp; a power conversion section adapted toconvert direct-current power into alternating-current power and supplythe discharge lamp with the alternating-current power via the resonantcircuit section; a control section adapted to change a frequency of thealternating-current power in a stepwise manner with a frequency, whichis different from a frequency causing a resonance of the resonantcircuit section, intervening between frequency values of the frequencychanged in a lighting start period until the discharge lamp reaches astationary lighting state; a detection section adapted to detect one ofa resonant output current and a resonant output voltage of the resonantcircuit section; and a lighting detection section adapted to detectlighting of the discharge lamp, wherein if a change in one of theresonant current and the resonant voltage detected by the detectionsection is switched from increase to decrease in a first time period ina process of changing the frequency of the alternating-current power inthe stepwise manner, the control section sets the frequency of thealternating-current power to the frequency in a previous step, and thelighting detection section detects lighting of the discharge lamp in asecond time period after the first time period.
 20. A discharge lamplighting device comprising: a resonant circuit section connected to adischarge lamp; a power conversion section adapted to convertdirect-current power into alternating-current power and supply thedischarge lamp with the alternating-current power via the resonantcircuit section; a control section adapted to change a frequency of thealternating-current power in a stepwise manner with a frequency, whichis different from a frequency causing a resonance of the resonantcircuit section, intervening between frequency values of the frequencychanged in a lighting start period until the discharge lamp reaches astationary lighting state, wherein the frequency different from thefrequency causing the resonance of the resonant circuit section is lowerthan the frequency causing the resonance of the resonant circuitsection, and higher than a frequency at which a current supplied from apower conversion section adapted to supply the alternating-current poweris one of equal to and lower than a predetermined value.
 21. A dischargelamp lighting device adapted to supply a discharge lamp withalternating-current power via a resonant circuit section to therebystart discharge of the discharge lamp to light the discharge lamp, thedischarge lamp lighting device comprising: a control section adapted tochange a frequency of the alternating-current power in a stepwise mannerwith a frequency, which is different from a frequency causing aresonance of the resonant circuit section, intervening between frequencyvalues of the frequency changed in a lighting start period until thedischarge lamp reaches a stationary lighting state, wherein thefrequency different from the frequency causing the resonance of theresonant circuit section is lower than the frequency causing theresonance of the resonant circuit section, and higher than a frequencyat which a current supplied from a power conversion section adapted tosupply the alternating-current power is one of equal to and lower than apredetermined value.